The invention relates to an identification arrangement or device in the form of a label-like or tag-like structure affixable to an article and comprising at least one inductive element formed from planar conductive paths and a capacitive element formed from superimposed conductive path parts and a dielectric interposed therebetween, which forms a closed resonant circuit with the inductive element, the conductive paths being arranged in at least two surfaces which are superimposed by folding together, as well as to a method for its manufacture.
From German Auslegeschrift No. 28 26 861 identification arrangements or devices are already known which essentially contain an electrical parallel resonant circuit and are arranged to produce in a high frequency electromagnetic field characteristic signals which enable their recognition. Such passive identification arrangements are utilized as security elements and as recognition sensors in merchandise security systems, in particular theft security systems.
If such arrangements are required in very large quantities, the manufacturing costs of such arrangements as well as their handling costs play a wholly decisive role in the economic use of the system. A substantial reduction of handling costs is possible by one-time use of such arrangements; an important prerequisite for this is extremely low manufacturing costs.
From German Offenlegungsschrift No. 25 23 002, tag-like identification arrangements are known which are manufactured in that conductive paths are etched out of various strong metal foils which are laminated on both sides of a flexible electrically insulating carrier foil. The etched-out conductive paths form the inductive element, whilst the capacitive element is formed by stamped out conductive surfaces which lie opposite one another and are mutually separated by the intermediate insulating carrier foil. Since after the etching the conductive path regions on both sides of the carrier foil have no conductive connection with each other, such a connection must be performed in a suitable manner in the form of a through-contact through the thin and elastic carrier foil. This process is complicated from the point of view of manufacturing technology, occupies a relatively long time, and does not produce a satisfactory durable contact, as continual investigations of arrangements made in such manner show. In addition, the double-sided etching process--particularly with simultaneous processing of layers of various thicknesses--is expensive. The through contact region cannot be imprinted as it would be damaged.
There are moreover limitations to the known method of manufacture in that the dielectric layer used therein cannot be made arbitrarily thin because during the etching process it must, as carrying substrate, have a certain minimum stability. This leads to relatively large metal surfaces as capacitor layers which limit the resonant quality of such constructions as a result of the eddy current losses caused thereby and sets thereby a limit to arbitrary miniaturization of such arrangements.
The identification arrangement mentioned in the introduction is already known from German Offenlegungsschrift No. 31 43 208.5.
The invention is based on the idea of arranging conductive paths by folding together of a conductor path construction which is connected or divided into at least two parts, at least partially overlapping and/or crossing over one another in such manner that in each case performance of a contact is not necessary and the necessary resonant circuit capacitance of such a resonant construction is formed by selective introduction of dielectric layers between conductive path parts folded on each other in concentrated or distributed form. Since not only the conductive paths but also the dielectric layers can be made very thin, the thickness of a finished identification arrangement is also very small without the need to forego sufficient circuit inductance and circuit capacitance.
An object of the invention is to create an identification arrangement and a method for its manufacture which on the one hand enable economically favourable mass-production so that such identification arrangements are suitable for one-way use, and on the other hand provide sufficiently low tolerances of the resonant frequency and resonant quality and a high reliability through the absence of contacts pressed through an insulating foil.
This object is achieved in that the conductor path parts forming the capacitive element mutually overlap and are identical to at least some extent with the conductor paths forming the inductive element.
Further advantageous embodiments of the identification arrangement according to the invention are described in claims 2 to 28.
The various embodiments of the method according to the invention are described in claims 29 to 42.
The identification arrangement according to the invention is applicable particularly to security and control systems such as merchandising security systems, object security systems, document security systems, entry control systems, event control systems (e.g. parking systems), data security systems and permit control systems.